Electronic timepiece

ABSTRACT

An electronic timepiece includes a mode setter that sets an azimuth mode in which the azimuth is measured and displayed, at least one indicating hand that operates when the azimuth mode is set, markings at which the indicating hand points, a stepper motor including a rotor, a wheel train that moves the indicating hand in synchronization with the rotor, a magnetism sensor, and an azimuth measurer that measures magnetism with the magnetism sensor when the azimuth mode is set and acquires the azimuth based on the measured magnetism information. The reduction ratio of the wheel train is so set that the indicating hand moves by the distance corresponding to one marking when the rotor makes N turns, where N is an integer greater than or equal to 1, and the azimuth measurer measures the magnetism during the period for which the indicating hand stationarily points at any of the markings.

CROSS-REFERENCE TO RELATED APPLICATION

This nonprovisional application claims the benefit of Japanese PatentApplication No. 2017-058231 filed Mar. 23, 2017, the enter disclosurewhich is incorporated herein by reference.

BACKGROUND 1. Technical Field

The present invention relates to an electronic timepiece having anazimuth measuring function.

2. Related Art

There has been a known analog electronic timepiece having a compassfunction of measuring the azimuth (see U.S. Pat. No. 6,992,481, forexample).

The analog electronic timepiece described in U.S. Pat. No. 6,992,481measures magnetism with a sensor and acquires the azimuth based on themeasured magnetism. The electronic timepiece further includes a steppermotor that drives the second hand. The stepper motor includes a two-polerotor formed of a permanent magnet and causes the rotor to pivot onestep of 180° every one second. According to the configuration describedabove, when the magnetism is measured, the following cases occur: a casewhere the rotor is oriented in a first direction; and a case where therotor is oriented in a second direction shifted from the first directionby 180°. In these cases, magnetic fields different from each other areproduced.

When the magnetic field produced in the timepiece varies whenever themagnetism is measured, the azimuth cannot be measured with accuracy. Toavoid the problem, the analog electronic timepiece described in U.S.Pat. No. 6,992,481 detects the orientation of the rotor before themagnetism measurement. When the orientation of the rotor is a specifiedorientation, the magnetism is measured with the orientation of the rotorunchanged. On the other hand, when the orientation of the rotor is notthe specified orientation (when the orientation is shifted from thespecified orientation by 180°), the magnetism is measured after therotor is caused to pivot by 180° so that the orientation of the rotor isthe specified orientation. As described above, whenever the magnetism ismeasured, the orientation of the rotor is caused to be the specifiedorientation, whereby the same-state magnetic field produced in thetimepiece is measured.

In the analog electronic timepiece described in U.S. Pat. No. 6,992,481,the orientation of the rotor is detected before the magnetism ismeasured, and when the orientation of the rotor is not the specifiedorientation, the rotor is caused to pivot, followed by the magnetismmeasurement. The procedure undesirably requires a long time for azimuthmeasurement.

SUMMARY

An advantage of some aspects of the invention is to provide anelectronic timepiece capable of shortening the period required forazimuth measurement.

An electronic timepiece according to an aspect of the invention includesa mode setter that sets an azimuth mode in which an azimuth is measuredand displayed, at least one indicating hand that operates when theazimuth mode is set, markings at which the indicating hand points, astepper motor including a rotor, a wheel train that moves the indicatinghand in synchronization with the rotor, a magnetism sensor, and anazimuth measurer that measures magnetism with the magnetism sensor whenthe azimuth mode is set and acquires the azimuth based on the measuredmagnetism information. A reduction ratio of the wheel train is so setthat the indicating hand moves by a distance corresponding to onemarking when the rotor makes N turns, where N is an integer greater thanor equal to 1, and the azimuth measurer measures the magnetism during aperiod for which the indicating hand stationarily points at any of themarkings.

In the aspect of the invention, the reduction ratio of the wheel trainis so set that the indicating hand moves over the distance correspondingto one marking segment when the rotor makes N turns. Therefore, when theindicating hand stationarily points at any of the markings, the rotor isalways oriented in the same direction. Causing the azimuth measurer tomeasure the magnetism during the period for which the indicating handstationarily points at any of the markings therefore allows magnetismmeasurement with the magnetic field produced in the timepiece maintainedin the same state whenever the magnetism is measured, whereby theazimuth can be measured with accuracy.

Further, since the rotor is not required to pivot before the magnetismmeasurement, the period necessary for the azimuth measurement can beshortened.

In the electronic timepiece according to the aspect of the invention, itis preferable that the mode setter sets a calibration mode in which acorrection value for correcting the magnetism information is acquired,that the electronic timepiece further includes a calibrator thatacquires the correction value when the calibration mode is set bymeasuring the magnetism with the magnetism sensor during a period forwhich the indicating hand stationarily points at any of the markings,and that the azimuth measurer corrects the magnetism information basedon the correction value to acquire the azimuth.

The correction value is, for example, a magnetic field produced in thetimepiece (offset magnetic field). The offset magnetic field can beacquired, for example, by measuring the magnetism with the orientationof the electronic timepiece changed.

According to the aspect of the invention with this configuration, whenthe magnetism is measured to acquire the correction value, the rotor isallowed to have the same orientation with which the azimuth measurementis performed. The magnetic field produced in the timepiece can thereforebe maintained in the same state as that in the azimuth measurement,whereby an appropriate correction value can be acquired. Correcting themagnetism information measured in the azimuth measurement by using thecorrection value to acquire the azimuth therefore allows accurateazimuth measurement.

It is preferable that the electronic timepiece according to the aspectof the invention further includes a mode hand provided separately fromthe indicating hand, an azimuth mode marking at which the mode handpoints when the azimuth mode is set, a calibration mode marking at whichthe mode hand points when the calibration mode is set, and a steppermotor for the mode hand including a rotor for the mode hand, and thatthe mode hand moves between the azimuth mode marking and the calibrationmode marking when the rotor for the mode hand makes n turns, where n isan integer greater than or equal to 1.

In the aspect of the invention with this configuration, the mode handmoves between the azimuth mode marking and the calibration mode markingwhen the rotor for the mode hand makes n turns. The rotor for the modehand is therefore allowed to have the same orientation both in the casewhere the mode hand points at the azimuth mode marking and the casewhere the mode hand points at the calibration mode marking. The magneticfield produced in the timepiece is therefore allowed to have the samestate both in the azimuth measurement and the correction valueacquisition. Therefore, even when the stepper motor for the mode hand isprovided, an appropriate correction value can be acquired.

It is preferable that the electronic timepiece according to the aspectof the invention further includes a second hand provided separately fromthe indicating hand, second markings at which the second hand points,and a stepper motor for the second hand that includes a rotor for thesecond hand and moves the second hand over a distance corresponding toone marking when the rotor for the second hand is caused to make a halfturn every one second, and that the second hand stops with the rotor forthe second hand having a predetermined orientation when the azimuth modeis set.

Since the indicating hand described above moves over the distancecorresponding to one marking segment when the rotor makes at least oneturn, the electric power required to move the indicating hand over thedistance corresponding to one marking segment is greater than, forexample, in a case where the indicating hand moves over the distancecorresponding to one marking segment when the rotor makes a half turn.Therefore, in a case where the indicating hand is, for example, thesecond hand, which moves over the distance corresponding to one markingsegment every one second, the electric power consumed by the timepieceincreases.

In contrast, in the aspect of the invention with the configurationdescribed above, the second hand is provided separately from theindicating hand described above, and the second hand moves over thedistance corresponding to one marking segment when the rotor for thesecond hand makes a half turn every one second. The electric powerconsumed by the timepiece can therefore be lowered as compared with thecase where the indicating hand is the second hand.

Further, according to the aspect of the invention with the configurationdescribed above, when the azimuth mode is set, the rotor for the secondhand is stationary and has a predetermined orientation. The magnetismcan therefore be measured with the magnetic field produced in thetimepiece maintained in the same state whenever the magnetism ismeasured, whereby the azimuth can be measured with accuracy.

It is preferable that the electronic timepiece according to the aspectof the invention further includes a second hand provided separately fromthe indicating hand, second markings at which the second hand points, astepper motor for the second hand that includes a rotor for the secondhand and moves the secondhand over a distance corresponding to onemarking when the rotor for the second hand is caused to make a half turnevery one second, and an orientation detector that detects anorientation of the rotor for the second hand, that the second hand movesevery one second when the azimuth mode is set, and that the azimuthmeasurer corrects the measured magnetism information in accordance withthe orientation of the rotor for the second hand to acquire the azimuth.

In the aspect of the invention with this configuration, since the secondhand is provided separately from the indicating hand described above,and the second hand moves over the distance corresponding to one markingsegment when the rotor for the second hand makes a half turn every onesecond, the electric power consumed by the timepiece can be lowered ascompared with the case where the indicating hand described above is thesecond hand.

Further, according to the aspect of the invention with the configurationdescribed above, the second hand can display the second even during theperiod for which the azimuth mode is set.

Moreover, since the second hand moves even during the period for whichthe azimuth mode is set, the rotor of the second hand does not alwayshave the same orientation when the magnetism is measured. Therefore, inthe aspect of the invention with the configuration described above, whenthe magnetism is measured, the orientation of the rotor for thesecondhand is detected, and the measured magnetism information iscorrected in accordance with the detected orientation of the rotor forthe secondhand, followed by azimuth acquisition. A decrease in theaccuracy in the azimuth measurement can thus be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a front view of an electronic timepiece according to a firstembodiment of the invention.

FIG. 2 is a block diagram showing the configuration of a movement in thefirst embodiment.

FIG. 3 shows the configuration of a motor for a center hand in the firstembodiment.

FIG. 4 is a flowchart showing an azimuth measurement action in the firstembodiment.

FIG. 5 is a front view if an electronic timepiece according to a secondembodiment of the invention.

FIG. 6 is a block diagram showing the configuration of a movement in thesecond embodiment.

FIG. 7 is a block diagram showing the function of a CPU in anotherembodiment of the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Embodiments according to the invention will be described below withreference to the drawings.

First Embodiment

FIG. 1 is a front view showing an electronic timepiece 1.

The electronic timepiece 1 includes an exterior case 3 and an hour hand11, a minute hand 12, a center hand 13, a dial 2, and a movement 6 (seeFIG. 2), which are accommodated in the exterior case 3, as shown in FIG.1.

The dial 2 is formed in a disc-like shape, and markings 2A, which are soprovided around the outer circumference of the dial 2 as to divide thecircumference thereof into 60 segments. A rotating shaft is provided atthe center of the dial 2 in a plan view, and the hour hand 11, theminute hand 12, and the center hand 13 (indicating hand) are attached tothe rotating shaft. The center hand 13 points at any of the markings 2Ato display the north cardinal point (bearing). That is, the northcardinal point is displayed in the unit of 6°. The hour hand 11 and theminute hand 12 each point at any of the markings 2A to display the hourand minute of the time.

The dial 2 is further provided with an opening 2B in a 6-o'clockposition with respect to the center of the dial 2 in a plan view viewedfrom the side facing the front surface of the timepiece. Lettersdisplayed by an LCD (liquid crystal display) 14, which is provided inthe movement 6 provided on the rear side of the dial 2, are visuallyrecognized through the opening 2B. The LCD 14 displays a mode in thepresent embodiment.

The exterior case 3 is provided with a crown 4, which is an externallyoperated member, and a button 5, which is another externally operatedmember.

Configuration of Movement

FIG. 2 is a block diagram showing the configuration of the movement 6.

The movement 6 includes a magnetism sensor 21, a motor 22 for thehour/minute hands, a motor 23 for the center hand, a wheel train 24 forthe hour/minute hands, a wheel train 25 for the center hand, the LCD 14,and a control circuit 30.

The magnetism sensor 21 is, for example, a three-axis magnetism sensor,measures magnetism to acquire magnetism information, and outputs theacquired magnetism information to the control circuit 30. The magnetismsensor 21 is disposed in an 8-o'clock position with respect to thecenter of the dial 2 in the plan view, as shown in FIG. 1.

The motor 23 for the center hand is formed of a two-pole stepper motor.

The motor 23 for the center hand includes a stator 231, which has arotor accommodating hole 231A, a rotor 232, which is pivotably disposedin the rotor accommodating hole 231A, a magnetic core (not shown) joinedwith the stator 231, and a coil 233, which is wound around the magneticcore, as shown in FIG. 3. The rotor 232 is so magnetized as to form twopoles (S and N poles), and the stator 231 is made of a magneticmaterial. A pair of inner notches 231B are so provided on the innercircumference of the rotor accommodating hole 231A of the stator 231 asto face each other in the radial direction of the hole. The rotor 232receives force that maintains the attitude of the rotor 232 in such away that a line segment along the direction in which the two magneticpoles, the N pole and the S pole, of the rotor 232 face each other isperpendicular to a line segment passing through the pair of innernotches 231B. The rotor 232 is therefore stationary with the aboveattitude maintained in a case where no current flows through the coil233.

When a motor drive pulse is supplied to the opposite terminals of thecoil 233 and current therefore flows through the coil 233, a magneticflux is produced in the stator 231. As a result, interaction between themagnetic poles created in the stator 231 and the magnetic poles of therotor 232 causes the rotor 232 to pivot by 180° (one step) in theforward or reverse direction. The rotor 232 thus pivots by the unit of180° whenever the motor drive pulse is supplied to the coil 233. Thatis, the rotor 232 alternately has one of two different orientationsshifted by 180° from each other.

The motor 22 for the hour/minute hands has the same configuration asthat of the motor 23 for the center hand shown in FIG. 3.

The motor 23 for the center hand is disposed in an 11-o'clock positionwith respect to the center of the dial 2 in the plan view, as shown inFIG. 1. The motor 22 for the hour/minute hands is disposed in a2-o'clock position with respect to the center in the plan view. Therotor 232 of the motor 23 for the center hand is located closer to themagnetism sensor 21 than the rotor of the motor 22 for the hour/minutehands when viewed from the side facing the front side of the timepiece.

The wheel train 25 for the center hand is formed of a plurality of gearsand moves the center hand 13 in synchronization with the rotor 232 ofthe motor 23 for the center hand.

The reduction ratio of the wheel train 25 for the center hand is so setthat the center hand 13 moves over the distance corresponding to onemarking segment when the rotor 232 makes one turn, that is, when therotor 232 pivots two steps. The configuration described above allows therotor 232 to always have the same orientation when the center hand 13points at any of the markings 2A. That is, in the timepiece, thedirection from the S pole toward the N pole (or direction from N poletoward S pole) is always fixed.

The wheel train 24 for the hour/minute hands is formed of a plurality ofgears and moves the hour hand 11 and the minute hand 12 insynchronization with the rotor of the motor 22 for the hour/minutehands.

The reduction ratio of the wheel train 24 for the hour/minute hands isso set that the minute hand 12 moves over the distance corresponding toone marking segment when the rotor makes one turn, that is, when therotor pivots two steps. The configuration described above allows therotor to always have the same orientation when the minute hand 12 pointsat any of the markings 2A.

Configuration of Control Circuit

The control circuit 30 includes a CPU (central processing unit) 31(processor), an RTC (real-time clock) 32, a driver 33 for thehour/minute hands, a driver 34 for center hand, an LCD driver 35, acrown operation detector 36, a button operation detector 37, a RAM(random access memory) 38, and a ROM (read only memory) 39.

The driver 33 for the hour/minute hands uses a clock signal outputtedfrom the RTC 32 to output motor drive pulses to the motor 22 for thehour/minute hands.

The driver 34 for center hand uses the clock signal to output motordrive pulses to the motor 23 for the center hand.

The LCD driver 35 outputs a drive signal to the LCD 14.

The crown operation detector 36 detects operation performed on the crown4 and outputs an operation signal according to the operation to the CPU31.

The button operation detector 37 detects operation performed on thebutton 5 and outputs an operation signal according to the operation tothe CPU 31.

The ROM 39 stores, for example, a program executed by the CPU 31.

The RAM 38 stores, for example, data required when the CPU 31 carriesout processes. For example, the RAM 38 stores an offset magnetic fieldrepresenting the magnetic field produced in the timepiece as acorrection value for correcting the magnetism information.

The CPU 31 executes the program stored in the ROM 39 to function as amode setter 311, an azimuth measurer 312, a calibrator 313, and adisplay controller 314.

The mode setter 311 sets, in accordance with operation performed on thecrown 4 and the button 5, an azimuth mode in which the azimuth ismeasured and displayed and a calibration mode in which the offsetmagnetic field described above is acquired.

The azimuth measurer 312 controls the magnetism sensor 21, when theazimuth mode is set, to measure the magnetism in accordance with theoperation performed on the button 5 and calculates and acquires theazimuth based on the measured magnetism information.

The calibrator 313 controls the magnetism sensor 21, when thecalibration mode is set, to measure the magnetism and calculates andacquires the offset magnetic field.

The display controller 314 controls the driver 33 for the hour/minutehands, the driver 34 for center hand, and the LCD driver 35 to controldisplay operation performed by the hour hand 11, the minute hand 12, thecenter hand 13, and the LCD 14.

The above functional portions will each be described in detail in thefollowing description of an azimuth measurement action and a calibrationaction.

Azimuth Measurement Action

For example, when the button 5 is pressed, the mode setter 311 sets theazimuth mode. At this point, the display controller 314 controls the LCDdriver 35 to cause the LCD 14 to display English letters “COMP,” whichmeans a compass, as shown, for example, in FIG. 1, to show that theazimuth mode has been set. It is noted that the hour hand 11 and theminute hand 12 keep displaying the hour and minute, and the center hand13 points at the 12-o'clock position.

When the azimuth mode is set, the electronic timepiece 1 performs theazimuth measurement action shown in the flowchart of FIG. 4.

The azimuth measurer 312 first evaluates whether or not the button 5 hasbeen pressed (step S11), as shown in FIG. 4. The azimuth measurer 312repeats the process in step S11 until the button 5 is pressed.

In the case where the button 5 has been pressed and the result of theevaluation in step S11 therefore is YES, the azimuth measurer 312activates the magnetism sensor 21 to measure the magnetism (step S12).During the magnetism measurement performed by the azimuth measurer 312,the center hand 13 and the minute hand 12 each point at any of themarkings 2A.

The azimuth measurer 312 then reads the offset magnetic field from theRAM 38 and corrects the measured magnetism information based on theoffset magnetic field (step S13). Specifically, the azimuth measurer 312removes an offset magnetic field component from the magnetisminformation and leaves only a geomagnetic component. The azimuthmeasurer 312 then calculates and acquires the north cardinal point basedon the corrected magnetism information (step S14).

The display controller 314 then controls the driver 34 for center handto cause the center hand 13 to point at the marking 2A corresponding tothe acquired north cardinal point to display the north cardinal point(step S15).

The mode setter 311 then evaluates whether or not the button 5 has beenpressed again (step S16). In a case where the result of the evaluationin step S16 is NO, the mode setter 311 proceeds to the process in stepS12. The processes in steps S12 to S15 are therefore repeatedly carriedout until the button 5 is pressed and the result of the evaluation instep S16 therefore becomes YES. In the process in step S12, themagnetism is measured, for example, every 0.5 seconds or 1 second.

When the button 5 is pressed and the result of the evaluation in stepS16 is therefore YES, the display controller 314 causes the center hand13 to point at the 12-o'clock position (step S17) and causes the LCD 14to stop displaying “COMP.” The mode setter 311 then deactivates theazimuth mode. The azimuth measurement action is thus terminated.

A timeout action (not shown) may be so added that the azimuth mode isdeactivated, for example, one or two minutes after the azimuth mode isset. The timeout action allows automatic deactivation of the azimuthmode even if a user forgets to deactivate the azimuth mode, wherebyuseless power consumption can be avoided.

Calibration

For example, when the button 5 is pressed with the crown 4 pulled onestep, the mode setter 311 sets the calibration mode. At this point, thedisplay controller 314 causes the LCD 14 to display English letters“CAL” to show that the calibration mode has been set.

When the calibration mode is set, the electronic timepiece 1 performsthe calibration action.

The calibrator 313 first activates the magnetism sensor 21 to measurethe magnetism. The display controller 314 then causes the LCD 14 todisplay a message that prompts the user to rotate the attitude of theelectronic timepiece 1 by 180°. After the user rotates the electronictimepiece 1 by 180°, when the user presses the button 5 again, thecalibrator 313 activates the magnetism sensor 21 again and measure themagnetism. During the magnetism measurement performed by the calibrator313, the center hand 13 and the minute hand 12 each point at any of themarkings 2A.

The calibrator 313 then calculates and acquires the average of the firstmeasured value and the second measured value. Rotating the attitude ofthe electronic timepiece 1 by 180° in accordance with the messagedescribed above before the second measurement is performed and acquiringthe average allow acquisition of magnetism information from which thegeomagnetic component is removed, that is, the offset magnetic field.The calibrator 313 then stores the acquired value as the offset magneticfield in the RAM 38.

Thereafter, when the crown 4 is pressed back to the zero-step position,the display controller 314 causes the LCD 14 to stop displaying “CAL”,and the mode setter 311 deactivates the calibration mode. Thecalibration action is thus terminated.

Advantageous Effect of First Embodiment

According to the present embodiment, when the magnetism is measured inthe azimuth mode, the rotor of each of the motor 23 for the center handand the motor 22 for the hour/minute hands is always oriented in thefixed direction. The magnetism can therefore be measured with themagnetic field produced in the timepiece maintained in the same statewhenever the measurement is performed, whereby the azimuth can bemeasured with accuracy. Further, since the rotors are not required topivot before the magnetism measurement, the period necessary for theazimuth measurement can be shortened.

According to the present embodiment, when the magnetism is measured inthe calibration mode, the rotor of each of the motor 23 for the centerhand and the motor 22 for the hour/minute hands is allowed to have thesame orientation with which the azimuth measurement is performed. Themagnetic field produced in the timepiece can therefore be maintained inthe same state as that in the azimuth measurement, whereby anappropriate offset magnetic field can be acquired. The azimuth cantherefore be measured with accuracy.

Second Embodiment

In the first embodiment, in which the center hand 13 moves over thedistance corresponding to one marking segment when the rotor 232 makesone turn (pivots two steps), electric power required to move the centerhand 13 over the distance corresponding to one marking segment isgreater, for example, than in a case where the center hand 13 moves overthe distance corresponding to one marking segment when the rotor 232makes a half turn (pivots one step). Therefore, for example, in a casewhere the center hand 13 is configured to function also as the secondhand in a normal mode, the frequency at which the center hand 13 isdriven increases, and the electric power consumed by the timepieceincreases accordingly.

In contrast, an electronic timepiece 1A according to a second embodimentincludes a small second hand 15 and a motor 26 for the small secondhand, which drives the small second hand 15, in place of the LCD 14, andthe small second hand 15 moves over the distance corresponding to onemarking segment when the rotor of the motor 26 for small second handmakes a half turn (pivots one step). The configuration described aboveallows reduction in the electric power consumed by the timepiece ascompared with the case where the center hand 13 is configured to displaythe second.

The electronic timepiece 1A according to the second embodiment will bedescribed below with reference to the drawings. The same components asthose of the electronic timepiece 1 according to the first embodimenthave the same reference characters and will not be described.

FIG. 5 is a front view showing the electronic timepiece 1A.

The dial 2 of the electronic timepiece 1A is provided with a smallwindow 2C located in a 6-o'clock position with respect to the center ofthe dial 2 in a plan view and having a circular shape when viewed fromthe side facing the front side of the timepiece, as shown in FIG. 5.Markings 2D (second markings) are so provided around the outercircumference of the small window 2C as to divide the circumferencethereof into 60 segments. A marking 2E (azimuth mode marking), whichindicates the azimuth mode, and a marking 2F (calibration mode marking),which indicates the calibration mode, are further provided on the outercircumference of the small window 2C. Further, English letters “COM,”which means a compass, are written in a region outside the marking 2E,and English letters “CAL,” which means the calibration, are written in aregion outside the marking 2F.

A rotating shaft is provided at the center of the small window 2C in theplan view, and the small second hand 15 is attached to the rotatingshaft. The small second hand 15 functions as the second hand in thenormal mode and points at any of the markings 2D to display the secondof the time. In the case where the azimuth mode or the calibration modeis set, the small second hand 15 functions as a mode hand; the smallsecond hand 15 points at the marking 2E when the azimuth mode is set andpoints at the marking 2F when the calibration mode is set.

FIG. 6 is a block diagram showing the configuration of a movement 6A ofthe electronic timepiece 1A.

The movement 6A includes a driver 41 for the small second hand, a motor26 for the small second hand, and a wheel train 27 for the small secondhand in place of the LCD driver 35 and the LCD 14.

The motor 26 for the small second hand is formed of a stepper motor andhas the same configuration as that of the motor 23 for the center handshown in FIG. 3. The motor 26 for the small secondhand is also referredto as a stepper motor for the second hand or a stepper motor for themode hand.

The motor 26 for the small second hand is disposed in a 5-o'clockposition with respect to the center of the dial 2 in the plan view, asshown in FIG. 5. The rotor of the motor 26 for the small second hand(also referred to as rotor for second hand or rotor for mode hand) islocated in a position more remote from the magnetism sensor 21 than therotor 232 of the motor 23 for the center hand when viewed from the sidefacing the front side of the timepiece.

The wheel train 27 for the small second hand is formed of a plurality ofgears and moves the small second hand 15 in synchronization with therotor of the motor 26 for the small second hand.

The reduction ratio of the wheel train 27 for the small second hand isso set that the small second hand 15 moves over the distancecorresponding to one of the segments of the markings 2D when the rotorof the motor 26 for the small second hand makes a half turn, that is,when the rotor pivots one step. Therefore, when the small second hand 15points at any of the markings 2D, the rotor described above does notalways have the same orientation but has either of the two orientationsdescribed above.

The driver 41 for the small second hand, which is provided in a controlcircuit 30A, is controlled by the display controller 314 and uses theclock signal outputted from the RTC 32 to output motor drive pulses tothe motor 26 for the small second hand.

In the present embodiment, since the small second hand 15 points at themarking 2E when the azimuth mode is set, the rotor of the motor 26 forthe small second hand always has the same orientation (predeterminedorientation) in the magnetism measurement.

Further, in the present embodiment, the markings 2E and 2F are soprovided as to overlap with the markings 2D with three markings 2Dbetween the markings 2E and 2F. That is, when the rotor of the motor 26for the small second hand makes two turns (pivots four steps), the smallsecond hand 15 moves between the marking 2E and the marking 2F.According to the configuration described above, the rotor of the motor26 for the small second hand has the same orientation both in the casewhere the small second hand 15 points at the marking 2E and the casewhere the small second hand 15 points at the marking 2F.

The arrangement of the markings 2E and 2F is not limited to thearrangement described above and only needs to be an arrangement in whichthe small second hand 15 moves between the marking 2E and the marking 2Fwhen the rotor described above makes n turns, where n is an integergreater than or equal to 1. Also in this case, the rotor described abovehas the same orientation both in the case where the small second hand 15points at the marking 2E and the case where the small second hand 15points at the marking 2F.

The electronic timepiece LA, when it starts the azimuth measurementaction, carries out the processes in steps S11 to S16, as in the firstembodiment. When the result of the evaluation in step S16 shows that thebutton 5 has been pressed, the display controller 314 causes the smallsecond hand 15 to display the second of the time, and the mode setter311 deactivates the azimuth mode.

The calibration action in the present embodiment is the same as that inthe first embodiment.

Advantageous Effect of Second Embodiment

According to the present embodiment, when the magnetism is measured inthe azimuth mode, the rotor of each of the motor 23 for the center hand,the motor 22 for the hour/minute hands, and the motor 26 for the smallsecond hand is always oriented in the fixed direction. The magnetism cantherefore be measured with the magnetic field produced in the timepiecemaintained in the same state whenever the measurement is performed,whereby the azimuth can be measured with accuracy. Further, since therotors are not required to pivot before the magnetism measurement, theperiod necessary for the azimuth measurement can be shortened.

According to the present embodiment, when the magnetism is measured inthe calibration mode, the rotor of each of the motor 23 for the centerhand, the motor 22 for the hour/minute hands, and the motor 26 for thesmall second hand is allowed to have the same orientation with which theazimuth measurement is performed. The magnetic field produced in thetimepiece can therefore be maintained in the same state as that in theazimuth measurement, whereby an appropriate offset magnetic field can beacquired. The azimuth can therefore be measured with accuracy.

OTHER EMBODIMENTS

The invention is not limited to the embodiments described above, andchanges, improvements, and other modifications to the extent that theadvantage of the invention is achieved fall within the scope of theinvention.

Variation 1

In the second embodiment described above, in the case where the azimuthmode is set, the small second hand 15 stationarily points at the marking2E, but not necessarily. For example, the small second hand 15 may keepdisplaying the second.

In this case, however, when the magnetism is measured in the azimuthmode, the rotor of the motor 26 for the small second hand does notalways have the same orientation. Therefore, to measure the magnetism,the orientation of the rotor is detected, and the measured magnetisminformation is corrected in accordance with the detected orientation ofthe rotor for azimuth acquisition.

That is, in Variation 1, a CPU 31B includes not only the mode setter311, the azimuth measurer 312, the calibrator 313, and the displaycontroller 314 but an orientation detector 315, which detects theorientation of the rotor of the motor 26 for the small second hand. Theorientation detector 315 detects the orientation of the rotor describedabove, for example, by evaluating whether the second at which the smallsecond hand 15 points is an odd second or an even second.

Further, in the case where the calibration mode is set, the electronictimepiece carries out not only the process of acquiring the offsetmagnetic field but the process of acquiring an orientation correctionvalue for correcting the magnetism information in accordance with theorientation of the rotor of the motor 26 for the small second hand.

Specifically, the calibrator 313 activates the magnetism sensor 21 withthe rotor described above having one of the two orientations describedabove to measure the magnetism. The display controller 314 then controlsthe driver 41 for the small secondhand to cause the rotor describedabove to pivot by 180° (one step). The calibrator 313 then measures themagnetism again.

The calibrator 313 then calculates the difference between the firstmeasured value and the second measured value and stores the differenceas the orientation correction value in the RAM 38.

In the azimuth measurement action, when the magnetism information iscorrected in step S13, the orientation detector 315 detects theorientation of the rotor of the motor 26 for the small second hand. Theazimuth measurer 312 then evaluates whether or not the orientation ofthe rotor coincides with the orientation of the rotor at the time ofacquisition of the offset magnetic field, and when they coincide witheach other, the magnetism information is corrected based on the offsetmagnetic field. On the other hand, when they do not coincide with eachother, the magnetism information is corrected based on the offsetmagnetic field and the orientation correction value.

A decrease in the accuracy in the azimuth measurement can thus besuppressed.

When the magnetism information is corrected in accordance with theorientation of the rotor, the accuracy in the azimuth measurement lowersin some cases due to a correction error. In Variation 1, however, sincethe rotor of the motor 22 for the hour/minute hands and the rotor 232 ofthe motor 23 for the center hand always have the same orientation, nocorrection according to the orientations of the rotors is performed.Therefore, the effect of the correction error can be reduced as comparedwith a case where correction is performed in consideration of theorientations of all rotors, whereby a decrease in the accuracy of theazimuth can be suppressed.

Variation 2

In each of the embodiments and the variation, the reduction ratio of thewheel train 25 for the center hand is so set that the center hand 13moves over the distance corresponding to one marking segment when therotor 232 makes one turn, but not necessarily. That is, the reductionratio only needs to be so set that the center hand 13 moves over thedistance corresponding to one marking segment when the rotor 232 makes Nturns, where N is an integer greater than or equal to 1. According tothe configuration described above, when the center hand 13 points at anyof the markings 2A, the rotor 232 always has the same orientation.

Similarly, the reduction ratio of the wheel train 24 for the hour/minutehands only needs to be so set that the minute hand 12 moves over thedistance corresponding to one marking segment when the rotor of themotor 22 for the hour/minute hands makes N turns.

Variation 3

In each of the embodiments and the variations, the reduction ratio ofthe wheel train 24 for the hour/minute hands is so set that the minutehand 12 moves over the distance corresponding to one marking segmentwhen the rotor of the motor 22 for the hour/minute hands makes N turns,but not necessarily.

That is, the rotor of the motor 22 for the hour/minute hands is locatedin a position more remote from the magnetism sensor 21 than the rotor232 of the motor 23 for the center hand. The effect of the rotor of themotor 22 for the hour/minute hands on the accuracy in the azimuthmeasurement is smaller than that of the rotor 232 of the motor 23 forthe center hand. Therefore, in a case where the effect of the rotor ofthe motor 22 for the hour/minute hands on the measurement accuracy issmall, the rotor does not always have the same orientation in themagnetism measurement. In this case, for example, the reduction ratio ofthe wheel train 24 for the hour/minute hands is so set that the minutehand 12 moves over the distance corresponding to one marking segmentwhen the rotor of the motor 22 for the hour/minute hands pivots by 180°(one step), and the consumed electric power can be lowered accordingly.It is noted in this case that the magnetism information may be correctedin accordance with the orientation of the rotor of the motor 22 for thehour/minute hands in the azimuth measurement, as in Variation 1.

Variation 4

In the first embodiment described above, the center hand 13 points atthe 12-o'clock position in the normal mode, but not necessarily. Forexample, the center hand 13 may point at any of the markings 2A todisplay the second of the time. That is, the center hand 13 may beallowed to function as the second hand. In this case, the motor 23 forthe center hand makes one turn (pivots two steps) every one second, andthe center hand 13 moves over the distance corresponding to one markingsegment every one second.

What is claimed is:
 1. An electronic timepiece comprising: a mode setterthat sets an azimuth mode in which an azimuth is measured and displayed;at least one indicating hand that operates when the azimuth mode is set;markings at which the indicating hand points; a stepper motor includinga rotor; a wheel train that moves the indicating hand in synchronizationwith the rotor; a magnetism sensor; and an azimuth measurer thatmeasures magnetism with the magnetism sensor when the azimuth mode isset and acquires the azimuth based on the measured magnetisminformation, wherein a reduction ratio of the wheel train is so set thatthe indicating hand moves by a distance corresponding to one markingwhen the rotor makes N turns, where N is an integer greater than orequal to 1, and the azimuth measurer measures the magnetism during aperiod for which the indicating hand stationarily points at any of themarkings.
 2. The electronic timepiece according to claim 1, wherein themode setter sets a calibration mode in which a correction value forcorrecting the magnetism information is acquired, the electronictimepiece further comprises a calibrator that acquires the correctionvalue when the calibration mode is set by measuring the magnetism withthe magnetism sensor during a period for which the indicating handstationarily points at any of the markings, and the azimuth measurercorrects the magnetism information based on the correction value toacquire the azimuth.
 3. The electronic timepiece according to claim 2,further comprising: a mode hand provided separately from the indicatinghand; an azimuth mode marking at which the mode hand points when theazimuth mode is set; a calibration mode marking at which the mode handpoints when the calibration mode is set; and a stepper motor for themode hand including a rotor for the mode hand, wherein the mode handmoves between the azimuth mode marking and the calibration mode markingwhen the rotor for the mode hand makes n turns, where n is an integergreater than or equal to
 1. 4. The electronic timepiece according toclaim 1, further comprising: a second hand provided separately from theindicating hand; second markings at which the second hand points; and astepper motor for the secondhand that includes a rotor for the secondhand and moves the second hand over a distance corresponding to onemarking when the rotor for the secondhand is caused to make a half turnevery one second, wherein the second hand stops with the rotor for thesecond hand having a predetermined orientation when the azimuth mode isset.
 5. The electronic timepiece according to claim 1, furthercomprising: a second hand provided separately from the indicating hand;second markings at which the second hand points; a stepper motor for thesecondhand that includes a rotor for the second hand and moves thesecond hand over a distance corresponding to one marking when the rotorfor the secondhand is caused to make a half turn every one second; andan orientation detector that detects an orientation of the rotor for thesecond hand, wherein the second hand moves every one second when theazimuth mode is set, and the azimuth measurer corrects the measuredmagnetism information in accordance with the orientation of the rotorfor the second hand to acquire the azimuth.